Difference between leaflet Marker and mapbox featureLayer - leaflet

Question

I understood that I can use the general Leaflet layer, and the more advanced map-box featureLayer, that provides useful functions as the filter.
However, I don't understand the difference between
marker = L.Marker (new L.LatLng(lat, lng),
{
icon: L.mapbox.marker.icon(
{'marker-color': 'fc4353'
'marker-size': 'large'
}),
title: name,
});
map.addLayer(marker);
and
var poijson = {
"type": "Feature",
"geometry": {
"type": "Point",
"coordinates": [lng, lat]
},
"properties": {
"title": poi.name,
"marker-color": "#fc4353",
"marker-size": "large"
}
};
map.featureLayer.setGeoJSON(geojson);
Is it just the same?
[UPDATE]
Moreover, if I had many markers, should I add a new layer for each marker? It seems not a good thing for performance..
For instance, If I do:
var pois; //loaded with pois info
var geojson=[]; //will contain geojson data
for (p=0; p< pois.length; p++)
{
var poi = pois[p];
var poijson =
{
"type": "Feature",
"geometry":
{
"type": "Point",
"coordinates": [poi.lng, poi.lat]
}
};
geojson.push(poijson);
}
map.featureLayer.setGeoJSON(geojson);
Does it will create many layers for each poi, or just one layer with all the markers?
thank you

Answer 1

When you add a marker to a Leaflet map via map.addLayer(marker);, the marker is added to the 'leaflet-maker-pane'. The markers are plain images/icons.
You can use a geoJSON layer to draw GIS features: points, lines, polygons, etc.
See here: http://leafletjs.com/examples/geojson.html
Mapbox's featureLayers is just an extension to Leaflet's geoJSONLayer
To add multiple markers, call addMarker multiple times. Leaflet will create a new layer for each of the markers. Each marker will be added as an image element to the leaflet-marker-pane div:
http://bl.ocks.org/d3noob/9150014
Updated response:
If you add a GeoJSON layer with multiple features, Leaflet will create separate layer for each of the features. You can inspect the layers of the map by calling map._layers after adding the GeoJSON Layer.
marker.addTo(map) and map.addLayer(marker) are doing the same thing.
Here's the addTo function taken from the source
addTo: function (map) {
map.addLayer(this);
return this;
},